Recently, to cope with rapid diffusion of optoelectronics technology into such as digital consumer electronics and needs for a high-precision, highly functional product, a crystalline material such as Si, Ge, or CaF2, and a hard and brittle material such as a cemented carbide mold or glass are used, and an ultra precision diamond cutting tool is used to cut these materials with high precision. An example of the cutting tool is a diamond cutting tool using a mono crystalline diamond tip as a cutting edge. As a specific example of the diamond tip, there is a diamond tip having a conical rake face to finish with good shape accuracy and surface roughness when turning a brittle material to have a curved surface (see for example Japanese Patent Laying-Open No. 63-237803 (Patent Document 1)).
Further, as a tool having a shape similar to that of the above-mentioned diamond tip, a mono crystalline cutting tool is provided in which a nose portion of the cutting tool is rounded to have a rake face with a negative rake angle, and the rake face is formed as a portion of a conical surface of a right circular cone (see for example Japanese Patent Laying-Open No. 64-64702 (Patent Document 2)).
Furthermore, a diamond cutting tool is provided in which an edge portion made of mono crystalline diamond is fixed to a tool body such that a rake face of the edge portion has a rake angle set negative in the range from −25° to −60° as shown in FIGS. 5A to 5C to cut a ductile and difficult-to-machine material such as high silicon aluminium or Ni-resist cast iron (see for example Japanese Patent Laying-Open No. 11-347807 (Patent Document 3)). In addition, as a method to perform ultra precision machining on a crystalline material such as a ZnSe lens, a method is provided by which a single cutting tool performs cutting from rough work to finish work using a mono crystalline diamond cutting tool having a rake angle of −20° to 20°, a clearance angle of 5° to 10°, and a cutting edge chamfered in a width of 0.5 to 2 μm to prevent the edge from getting chipped, as shown in FIGS. 6A and 6B (see for example Japanese Patent Laying-Open No. 10-43903 (Patent Document 4)).
Patent Document 1: Japanese Patent Laying-Open No. 63-237803
Patent Document 2: Japanese Patent Laying-Open No. 64-64702
Patent Document 3: Japanese Patent Laying-Open No. 11-347807
Patent Document 4: Japanese Patent Laying-Open No. 10-43903